title: No effects of slow oscillatory transcranial direct current stimulation (tDCS) on sleep-dependent memory consolidation in healthy elderly subjects.
abstract: BACKGROUND
  Studies in young healthy volunteers provided evidence of a beneficial impact of an anodal time-varied transcranial direct current stimulation (tDCS) during early slow wave rich sleep on declarative memory but not on procedural memory.
  
  
  OBJECTIVE
  The present study investigated whether sleep-dependent memory consolidation can also be affected by slow oscillating tDCS in a population of elderly subjects.
  
  
  METHODS
  26 subjects (69.1 years ± 7.7 years) received bi-frontal anodal stimulation (max. current density: 0.331 mA/cm(2)) during early NREM sleep in a double-blind placebo-controlled randomized crossover study. Stimulation effects on offline consolidation were tested by using a declarative and a procedural memory task. Furthermore, sleep stages were scored, EEG power was analyzed and spindle densities were assessed.
  
  
  RESULTS
  Independently from stimulation condition, performance in both memory tasks significantly decreased overnight. Stimulation revealed no significant effect on sleep-dependent memory consolidation. Verum tDCS was accompanied by significantly more time awake and significantly less NREM stage 3 sleep during five 1-min stimulation free intervals.
  
  
  CONCLUSIONS
  The results of the present study are in line with other studies showing that offline consolidation during sleep varies with age and is less pronounced in the elderly than in young or middle-aged subjects. Contrary to an almost identical positive study in young adults, slow oscillatory tDCS applied to the elderly failed to show a beneficial effect on memory consolidation in the present study.
authors.affiliation: Competence Centre of Sleep Medicine, Charité - University Medicine, Campus Benjamin Franklin, Eschenallee 3, 14050 Berlin, Germany. Electronic address: torsten.eggert@charite.de.
authors.forename: Torsten
authors.initials: T
authors.lastname: Eggert
authors.forename: Hans
authors.initials: H
authors.lastname: Dorn
authors.forename: Cornelia
authors.initials: C
authors.lastname: Sauter
authors.forename: Michael A
authors.initials: MA
authors.lastname: Nitsche
authors.forename: Malek
authors.initials: M
authors.lastname: Bajbouj
authors.forename: Heidi
authors.initials: H
authors.lastname: Danker-Hopfe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000502:physiology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D017286:Polysomnography; D012890:Sleep / Q000502:physiology*
keywords: Dorsolateral prefrontal cortex; Elderly; Memory consolidation; Sleep; tDCS